1. Field of the Invention
This invention relates to organic optical waveguide devices which have improved barrier properties after having been coated with silicon monoxide, and then with silicon dioxide doped with certain metals.
2. Background of the Invention
In optical communication systems, messages are transmitted typically through optical fibers by carrier waves of optical frequencies that are generated by sources, such as lasers or light emitting diodes. There is much current interest in such optical communication systems because they offer several advantages over other communication systems, such as having a greatly increased number of channels of communication and the ability to use other materials besides expensive copper cables for transmitting messages.
As the development of optical circuits proceeded, it became necessary to have optical waveguide devices which could couple, divide, switch and modulate the optical waves from one optical fiber to another, or from one waveguide device to another.
Organic materials, especially photopolymers, are attractive materials for the fabrication of optical waveguide devices. Organic materials typically have low absorption in the visible and near infra-red regions of the spectrum. Photopolymers, in particular, can be prepared by conventional coating techniques and so can be reproducibly manufactured in large volume at reasonable cost. In contrast to most inorganic materials, which have fixed sets of properties, the properties of photopolymers can be varied over wide ranges by changes in composition. Custom designed materials can be formulated for specific applications. In the fabrication of optical waveguide devices, complex waveguides of small dimensions can be manufactured by exposure through photomasks. Elaborate crystal growing and doping techniques are not required.
However, devices fabricated from organic materials may suffer from sensitivity to environmental factors, such as moisture, in high humidity atmospheric conditions, and oxygen. Thus, it is desirable for the device to comprise a good barrier to oxygen and/or water vapor. However, the most common barrier materials, which are polymer based resins such as ethylene vinyl alcohol copolymer or polyvinylidene chloride, although exhibiting good barriers to oxygen or moisture, do so only under ideal conditions.
U.S. Pat. No. 3,442,686 discloses multilayer structures having good barrier properties to gases and liquids, comprising a flexible transparent organic polymeric base film having thereon an adherent, transparent, flexible highly gas- and liquid-impermeable, moisture resistant, continuous glassy coating of inorganic material, and a sealable, flexible, transparent top coating of organic material. The preferred base films disclosed include polyethylene terephthalate film. The preferred glassy coatings are oxides of silicon and aluminum. Among the silicon oxides disclosed are silicon monoxide (SiO) and silicon dioxide (SiO.sub.2).
SiO is known to have better barrier properties than SiO.sub.2, but unfortunately SiO is much more expensive than SiO.sub.2. Effort has been made to use SiO.sub.2 coatings instead of SiO for economic reasons To some extent, the barrier properties of SiO.sub.2 can be improved by increased thickness, but there is a limit to this approach because of decreasing flexibility with increasing thickness.
U.S. Pat. No. 4,702,963 discloses a multilayer structure in which an adhesion layer is first vacuum deposited on a flexible polymer substrate, followed by vacuum deposition of a barrier layer. The adhesion layer can consist of Cr, which is preferred, Ta, Ni, Mo, oxides of Cr, alloys of Cr with Ta and Ni, codeposited mixtures of Cr and SiO having at least 20% by weight of Cr and a lead-alumina-silica glass composition. The patent discloses that the barrier is preferably silicon monoxide or silicon dioxide, and that when silicon dioxide is used, it may be mixed with glass modifiers such as oxides of Mg, Ba, and Ca, or with fluoride of alkaline earth metals, e.g., MgF.sub.2 to alter the color appearance of the overall structure.
U.S. Pat. No. 4,528,234 discloses a transparent multilayer structure comprising a plastic film having a vacuum deposited layer thereon of Al, Sn, Fe, Zn and/or Mg and then a top layer of a carboxyl-containing polyolefin layer. The metal layer is thin enough that the structure is transparent and the metal layer effects a secure bond between the plastic film and the carboxyl-containing layer. The patent also discloses that a vacuum deposited layer of silicon oxide or titanium oxide on one or both sides of the plastic film improves the barrier properties of the structure. In the Examples, both silicon monoxide and silicon dioxide are used as the barrier layer.
Japanese patent publication 62-156943 discloses a multilayer structure of multiple layers of film and multiple layers of a vacuum deposited metal such as Al, Zn, Cu, Pt, In, Sn, Au, Ag, Sn or metal compound such as silicon oxide. The layers of vacuum deposited metal or metal compound are separated from one another by a layer of film and/or a layer of adhesive.
U.S. patent application Ser. No. 07/513,354, filed Apr. 20, 1990, now U.S. Pat. No. 5,085,904 describes a process for making packaging film by sequentially applying layers of SiO and SiO.sub.2 to a resin substrate.